- because it's has active members who have or are working with it.
- because nobody has done Beginner's Latin Book by Collar and Daniell
- because there is no answer key for Beginner's Latin Book by Collar and Daniell
- because Episcopus says so.

Might I suggest something a little different. It depends, of course, on why you wish to study Latin. If for school work, then one of the two books you listed would be best. However, if (like me) you are studying as a hobby, then 'Learn Latin', by Peter Jones is a great and inexpensive introduction to the language. It teaches you, in fun, easy steps just enough (and no more!) to read excerpts from Catullus, some bible stuff, and parts of the Bayeux tapestry.
It covers quite a lot of the language, albeit superficially (the subjunctive takes only 4 pages), but having read the book, and done the exercises, as you progress through a more advanced course there's less feeling of 'omigod what's this?' than would otherwise be the case.
Just my 2 cents worth (which at current exchange rates is worth about 0.6 cents)

benissimus wrote:You can try going through both of them, or learning from one but doing the lessons from both for extra practice. I believe Barrius uses this technique.

Perfectly correct. I haven't progressed far in either (currently sidetracked by vocabulary project), but will resume. I especially like the extra practice found in C&D, and the fact that I can't cheat by looking at an answer key.

That forces me to respond on thread for verification, and I actually LEARN from my mistakes, as those that have been responded have been most gracious and helpful.